It will be appreciated that wireless networks have of late become overloaded due to the increasing number of users seeking to communicate with the cell towers. Various communications schemes have been proposed in order to multiplex the signals so that a large number of users can communicate with a given cell tower. In general for analog phones, the analog system provides one communication channel per user. As a result the analog service has become quickly overloaded with the large number of users seeking access to a cell tower. In order to accommodate the overloaded conditions, time division multiplexing, TDMA, frequency division multiplexing, FDMA, and code division multiplexing, CDMA, have been utilized to accommodate many users per tower. By multiplexing is meant multiple access in which the number of users communicating with the cell tower are organized so as not to interfere with one another, allowing an equitable sharing of the channel resource.
The original premise for TDMA type systems was a 3 to 1 advantage which has in general been realized. CDMA systems have initially promised a 20 to 1 advantage, but practically have been able to realize only a 3 to 1 advantage.
Additionally, satellite communications have required a certain amount of multiplexing to be able to accommodate users seeking to communicate through satellite uplinks and downlinks.
While the above-mentioned techniques for providing multiple access have proved useful in accommodating the increasing number of users, the number of users for wireless services has increased beyond the capacity of present systems to be able to accommodate them.
What is therefore necessary is a system that can accommodate simultaneous transmission from multiple users on the same frequency sharing the same time slot or channel. In order to be able to do this a system is required which can uncorrupt or separate simultaneously received signals. Not only is such a system required, it is also a requirement that the descrambling or separation be not computationally complex so that the computation can be carried out by processors in hand-held wireless units.
By way of further background, the original inception of multiple access (MA) for the wireless medium was dictated primarily by the need for simple receivers. MA schemes have traditionally assigned user's waveforms and timing protocols for the sole purpose of eliminating or minimizing interference among the various users that simultaneously access a shared wireless channel so that a simple matched-filter receiver can reliably detect any signal of interest. Specifically, time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA) and hybrid schemes force signals to be orthogonal in which there is no interference whatsoever, e.g. different users are assigned completely different timeslots or nearly orthogonal wideband signals such that there is negligible interference between any two signals sharing the same bandwidth. These systems work well within the primary original motivating constraint, namely, lack of computing capabilities in the receiver. Bandwidth, on the other hand, was plentiful relative to the original appetite for throughput.
Many decades later, three trends impact wireless communication: 1.) computing capabilities have improved many fold, 2.) the requirement for information throughput has increased exponentially, and 3.) the bandwidth available for typical MA systems has decreased. The imposition of orthogonal signal assignment coupled with limitations in available bandwidth result in MA systems that fall far short in capacity or throughput for today's needs.